Non-aqueous dispersions (RAD's) are well known in the art and typically consist of dispersions of addition polymers in a relatively non-polar non-aqueous liquid containing a steric stabilizing agent having dual affinity to both the dispersing and the dispersed media. For example, U.S. Pat. No. 3,198,759 teaches dispersions of addition polymers in a hydrocarbon medium. The hydrocarbon medium contains one or more aliphatic hydrocarbons containing dissolved therein an alkyd formed by either the direct esterification of a drying oil fatty acid with a dicarboxylic acid and a polyhydric alcohol or the indirect esterification of a drying oil by first alcoholization with a polyhydric alcohol and second esterification with a polybasic acid. European Patent Application 0 310 331 A2 teaches a non-aqueous dispersion of a soluble low molecular weight non-alkyd polymer which is attached or adsorbed onto a second non-soluble alkyd-free polymer. U.S. Pat. No. 4,530,957 teaches non-aqueous dispersions based on crosslinked acrylic polymer particles dispersed in a non-aqueous medium having a polymeric dispersion stabilizer. The polymeric dispersion stabilizer can be an alkyd which is formed by the self condensation of 12-hydroxystearic acid followed by a capping reaction with glycidyl methacrylate. U.S. Pat. No. 4,206,099 teaches non-aqueous dispersions of crosslinked polymer particles in a non-aqueous medium having an amphipathic steric stabilizing agent. The steric stabilizing agent can be a graft copolymer obtained by reacting a low molecular weight carboxyl group terminated condensate of linseed oil fatty acids and 12-hydroxystearic acid with acrylic copolymers. U.S. Pat. No. 3,779,977 teaches non-aqueous dispersions of an acrylonitrile copolymer in a liquid butadiene homopolymer or copolymer in a non-polar organic hydrocarbon liquid.
A review of those patents clearly shows that most NAD's have solids contents in a range generally less than 60% by weight and have relatively high volatile organic contents. Attempts to raise the solids content and lower the volatile organic content of these NAD's has led to compositions which either gell unacceptably, exhibit extremely high viscosities, are not stable for any appreciable length of time or exhibit extremely long and unacceptable dry times as air dry coatings.
In our attempts to decrease the VOC contents of NAD's, we have found that many alkyds produced via the traditional "alcoholysis" process (alcoholysis of a drying oil followed by reaction with a polybasic acid) have extremely high viscosities. The use of such alkyds in a non-aqueous dispersion can force the formulator to use a large amount of solvent to lower viscosity. This in turn causes the VOC of the NAD to increase unacceptably. Additionally, we have found that while many alkyds produced via the traditional "fatty acid esterification" process can be used to produce stable NAD's, they typically are limited in their ability to produce NAD's or coatings having NVM's greater than about 70% and VOC's less than about 350 g/l.
The present invention produces very high solids NAD's, greater than about 75% NVM, with very low VOC's of less than 305 g/l, which exhibit excellent stability, filterability, low grit, viscosity and tack-free and dry times when formulated as air dry coating compositions. These NAD's are the result of a selection process wherein certain critical parameters, described fully below, must be observed.